However, due to the particular properties of fluorine and its influence on the reactivity of fluorinated molecules, the chemistry of fluorine cannot be compared to its halogenated homologues. Technically, the very high reactivity of fluorine F2 and the aggressiveness of anhydrous and aqueous fluoric acid towards common materials require specific devices and reaction vessels. On a chemical point of view, the introduction of fluorine atoms or fluorinated groups (CF3, CHF2, OCF3, SCF3, CF3CO, CnF2n+1,...) to an organic substrate implies that specific methods must be devised for the design of the reactants and for the reactions which must be achieved. Similarly, the functionalization of fluorinated compounds frequently requires more or less important modifications of “classical” reactions. Only one natural stable fluorine isotope exists, the 19F isotope. One artificial radioactive isotope (18F), with a short half-life (t1/2 = 110 min), is now routinely produced; it is used to label bioactive molecules for medical imaging using PET (Positron Emission Tomography).